1. Field of the Invention
The present invention relates to a non-invasive body information measurement apparatus with which body information can be measured without resorting to invasive procedures, and in particular relates to a non-invasive body information measurement apparatus which can select a luminous energy level in a normal measurement period on the basis of a blood glucose level non-invasively measured during a calibration period.
2. Description of the Related Art
The number of patients with diabetes, which is a typical lifestyle disease, is on the rise around the world. Diabetic patients must constantly control their blood glucose in order to improve their quality of life by suppressing the complications associated with diabetes. To this end, these patients have to measure their blood glucose level on a regular basis every day under the supervision of a physician.
A common way to measure blood glucose is to use an invasive type of blood glucose measurement apparatus, which pricks the finger of the patient, collects a blood sample, and measures the blood glucose level. With this invasive blood glucose measurement apparatus, however, pricking the finger to collect a blood sample involves pain and inconvenience, entails the risk of infection, and so forth, and therefore a non-invasive blood glucose measurement apparatus has been proposed that does not require the collection of a blood sample.
As an example of this non-invasive blood glucose measurement apparatus, a “system for measuring a biological parameter by means of photoacoustic interaction” that makes use of a photoacoustic effect has been proposed (see Patent Document 1 (WO 98/38904), for example).
With this “system for measuring a biological parameter by means of photoacoustic interaction” that makes use of a photoacoustic effect, light of a wavelength that is absorbed by glucose is emitted from the biological measurement system and directed at a part of the body, such as a fingertip, and the emitted light is converged onto a relatively small focal area within the body. Also, the converged light is generally absorbed by glucose, and is converted into kinetic energy in tissue within the focal region and the adjacent region.
The kinetic energy converted in the tissue raises the temperature and pressure of the absorbing tissue region, and generates an acoustic wave. This acoustic wave will hereinafter be referred to as a “photoacoustic wave signal.” The photoacoustic wave signal radiates out from the absorbing tissue region and is detected by an acoustic sensor provided to the biological measurement system. This acoustic sensor is installed so as to be in contact with the body surface. The intensity of the photoacoustic wave signal is a function of the amount of glucose in the absorbing tissue region, and the intensity measured by the sensor is used to determine the blood glucose level.